Commonly used involute engagement of gearwheels, along with all its advantages, has a number of drawbacks, such as insufficient load carrying capacity of teeth due to small curvature of flanks, comparatively high losses related to the presence of sliding friction (see Baturin A. T., Itskovich G. M. and oth. Machine parts, M. Mashinostroyeniye, 1970, p. 264). Moreover, involute engagement has restrictions according to the value of gear ratio for one stage. In practice the gear ratio of a single-stage gearbox seldom exceeds 7. All these drawbacks stipulate the search of new types of engagement.
The Novikov's engagement is known (see also there), where a linear contact of teeth is replaced by a point contact, and the transverse reconjugation is replaced by axial. This engagement has convex-concave helical teeth with opposite direction of a helix and with initial contact in a point, which is transmitted parallel to gearwheel axis under rotation. Profiles in the face section are drawn by circular arcs and have curvature of opposite signs. Rolling prevails in Novikov's engagement, that is why it has greater efficiency and possesses higher contact strength than the involute engagement at the same main dimensions. However, they have the increased sensitivity to variation of interaxial distance of gearwheels, high vibroacoustic activity, low design versatility, all this restricts the area of practical application of the engagement (see Zhuravlev G. A. Impropriety of physical fundamentals of Novikov's engagement as the reason of limitation of its application//Gearboxes and drives 2006-#1(04). —pp. 38-45).
Involute helical engagement (SU 1060835, U.S. Pat. No. 3,247,736) with the decreased tooth number of a smaller gearwheel—pinion—allows to increase the gear ratio at the same interaxial distances. In particular, a pinion can be manufactured with one tooth, having an involute profile in the normal section, and the gear ratio will be equal to a tooth number of the greater gearwheel. For this purpose a correction of helical teeth with the involute profile of the pinion and gearwheel is necessary, and it is necessary to perform the different correction here for driving and driven gearwheels (U.S. Pat. No. 3,247,736). We take this engagement as the prototype for the first version of the invention.
Production of a pinion with one helical tooth of a corrected involute profile has manufacturing difficulties, and the presence of points of inflection in the tooth profile, which are stress concentrators, decreases the strength and load carrying capacity of the engagement.
Engagement of assembled gearwheels is known, as, for example, in SU 911069, chosen as the prototype for the second version of the invention. The assembled gearwheel represents the set of at least three rigidly interconnected gear rims, their face profiles are turned with respect to each other at equal angles with the pitch, equal to the gearwheel angular tooth pitch angle divided by the number of rims in the gearwheel. Features of such engagement are similar to features of a helical engagement of teeth with the corresponding profile and the drawbacks are the same as for the described above drawbacks of the involute engagement.
Various schemes of planetary mechanisms are known, designed with gearwheels of involute engagement. So, in particular, a four-link planetary mechanism is known according to James scheme (I. I. Artobolevskiy. Theory of mechanisms and machines, —M., <<Nauka>>, 1988, p. 156). The device contains two central gearwheels, one of which has external and the other—internal teeth, the carrier and satellites, meshing with both central gearwheels. In the gearbox with this scheme, the central gearwheel with external engagement is mounted on the driving shaft, the gearwheel with internal engagement is usually stationary, and the carrier is connected with the driven shaft. The gearing has high efficiency (97-98%) and rather simple design. This mechanism is chosen as the prototype for the first version of a planetary gear on basis of the proposed engagement.
The main drawback of this mechanism is the small gear ratio, determined as the ratio of radii of central gearwheels. In order to increase the gear ratio, it is necessary to increase significantly the diameter of the gearwheel with internal engagement, that increases abruptly overall dimensions and mass of a gear. In practice, the gear ratio of a mechanism with such scheme does not exceed 10.
A planetary mechanism according to David scheme is known with internal, external or mixed engagement (V. M. Shannikov. Planetary gearboxes with non centrode engagement. M., <<Mashgiz>>, 1948, p. 4, and also A. F. Kraynev. Reference dictionary on mechanisms, M. <<Mashinostroyeniye>>, 1987, p. 290), which we choose as the prototype for the second version of a planetary mechanism on basis of the proposed engagement. The planetary mechanism contains a carrier with double satellites and two central gearwheels. Each of central gearwheels is engaged with the first or the second gearwheel of double satellites correspondingly and forms the first and the second rows of involute engagement. Central gearwheels can be both with external engagement, or one can be with external and the other—with internal (mixed) engagement. The mechanism according to David scheme with external engagement for big gear ratios has a very low efficiency (less than 0.2% for the gear ratio 10000 according to the estimation given in the book V. M. Shannikov. Planetary gearboxes with non centrode engagement. M., <<Mashgiz>>, 1948, p. |4), and the mechanism with mixed engagement with rather high efficiency allows to obtain the gear ratio only within the limits 8-15.